The present invention is directed to the field of photographic materials containing scavenger molecules that are applied in the intermediate interlayers between the photographic sensitive emulsion layers.
Colour photographic elements are conventionally formed with blue, green and red recording layers coated on a film support. The blue, green and red recording layers contain radiation-sensitive silver halide emulsions that form a latent image if irradiated by blue, green and red light, respectively. The blue recording layer contains a yellow dye image-forming coupler, the green recording layer contains a magenta dye image-forming coupler and the red recording layer contains a cyan dye image-forming coupler. After the photographic element is exposed by an image, it is processed in a colour developer, which contains a colour developing agent that is oxidised by the selective reduction of the silver in the silver halide grains with the formation of the silver latent image. The oxidised colour developing agent then reacts with the dye image-forming coupler in the vicinity of the developed grains to produce an image dye. Yellow (absorbs blue light), magenta (absorbs green light) and cyan (absorbs red light) image dyes are formed in the blue, green and red recording layers respectively. Subsequently the photographic element is bleached (i.e. developed silver is converted back to silver halide) in order to eliminate the neutral density attributable to developed silver and then fixed (i.e. silver halide is removed) in order to provide stability during subsequent handling at room light conditions.
When processing is conducted as noted above, negative dye images are produced. To produce a viewable positive dye image and hence to produce a visual approximation of the hues of the subject photographed, white light is typically passed through the colour negative image to expose a second photographic element also having blue, green and red recording layers as described above, usually coated on a white reflective paper support. The second element is commonly referred to as a colour print element and the process of exposing the colour print element through the image bearing colour negative element is commonly referred to as printing. Processing the colour print element at the same way as described above for the negative film support produces a viewable positive image that approximates that of the subject originally photographed.
Both photographic elements, the colour negative film and the colour positive paper supports, contain radiation-sensitive silver halide emulsions in the blue, green and red recording layers. Image dyes are formed by the reaction of the oxidised developer molecules with the dye image-forming coupler. The oxidised developer molecules can migrate easily from one colour recording layer into another colour recording layer, which will cause imbalances in colour reproduction because a wrong colour dye is generated in an other recording layer. This phenomenon is called colour mix or colour contamination. In order to prevent this diffusion travelling of the oxidised developers the photographic elements contain scavenger molecules which are able to neutralise the oxidised molecules and preventing that a colour coupler forms the wrong colour dye in an other recording layer. Sometimes a certain (limited) amount of colour mix may be desirable for a better appearance of the image. This makes the design of the interlayer a complicated matter. The scavenger molecules are conventionally present in the intermediate interlayers between the different colour recording layers of the colour negative film but also in the same way at the colour positive paper support. The scavenger molecules are dissolved in an oil-in-water emulsion and as such integrated in the interlayers. An important disadvantage of the scavenger oil-water emulsion is that by increasing the quantity of oil-water emulsion the sharpness quality is negatively influenced due to increased scattering chances.
It has been described in EP-A 576911 to couple functional carboxylic acid groups of Rxe2x80x94COOH compounds to the amine groups of gelatine
The coupling of scavenger molecules to a polymer compound has already been described in JP-4062548, said polymers being applied in the interlayers of photographic products. The use of water-soluble polymers (proteins, polyvinyl alcohol (PVA), polyvinyl glycol (PVG)) coupled to different scavenger molecules is disclosed. The scavenger modified polymer molecules in the interlayers result in reduced colour contamination effects while also the photographic sensitivity after ageing is improved versus the conventional recipes in which the scavenger molecules are dissolved in the oil-water emulsion of the interlayers. The amount of scavenger modified polymer per square meter is disclosed over a very broad range from 1 mg to 20 g per square meter.
The present invention is based upon the surprising insight that the use of a specific concentration range of scavenger moieties in a scavenger modified polymers in combination with specific values for the thickness of the interlayer layer, results in a highly effective scavenging function against the migrated oxidised developer molecules whereas we found that the concentration of scavenger should be limited to prevent reduction of the maximum density Dmax in the colour recording layer.
The specific combinations of layer thicknesses and scavenger concentrations, which combinations are used in accordance with the present invention are conveniently expressed by a single design parameter. In this interlayer design parameter, the dry thickness of the interlayer (called d) is combined with the concentration of scavenger moieties in the interlayer (called [scavenger]). It was found that the design parameter {[scavenger moiety].d2} predicts the scavenging extend of the migrated oxidised developer molecules. Using this new interlayer design parameter it has thus become possible to specify a range of specific thicknesses in combination with a specified concentration range of scavenger moieties in the interlayer for which acceptable colour contamination happens in the colour recording layers as well as no reduction of the maximum density Dmax, while the dye fading and the sharpness quality of each colour recording layer improve.
Accordingly the invention comprises in its broadest scope a photographic material, comprising a photographic support and color sensitive recording layers on top of said support, said recording layers being separated from each other by interlayers, wherein the interlayers are characterised by the color mix predictive product function {[scavenger moiety].d2} greater than 2.0*10xe2x88x9215 mmol m2/g. In preferred embodiments the value of the product function is larger than 5.0*10xe2x88x9215 mmol m2/g, most preferably larger than 10.0*10xe2x88x9215 mmol m2/g.
The present invention is in a preferred embodiment directed to a photographic material containing scavenger modified polymers comprising scavenger moieties linked to a water soluble polymer, which polymers are applied in the interlayers, so that a concentration of scavenger moieties in the scavenger modified polymer that is lower than 0.5 mmol/g total polymer in the interlayer. In preferred embodiments these values are lower than 0.30, most preferably lower than 0.15 mmol/g polymer.
One of the additional advantages of the present invention is, that photographic material can be provided having one or more interlayers, with a thickness and scavenger concentration that is exactly tuned to meet the required specifications with respect to Dmax and color mix. This makes it possible to provide materials having interlayer thicknesses that are smaller than those of conventional materials.
In the present invention the reactive group (carboxylic acid, amine) of the scavenger compound is linked with the reactive groups (amine, carboxylic acid) of the water-soluble polymer, preferably gelatine. To increase the load of scavenger in the preferred polymer, gelatine, it is also possible to use part of the abundantly available carboxylic groups of the gelatine by amidation with ethylene di-amine with the N-HydroxySuccinimide (NHS)/carbodiimide system. It is also possible to use the carboxylic groups of the gelatine and to connect these with the amino group of the scavenger. Therefore the gelatine is, initially, activated with a carboxylic activating agent. The activated carboxyl group reacts with an amine containing scavenger compound to form the modified gelatine, as described in EP-A 0 576 912.
In case it is preferred to increase the load of scavenger in the polymer even further, one or more spacers can be inserted between the scavenger moiety and the polymer.
The scavenger modified polymer is much more efficient to scavenge oxidised developer molecules, as compared with the scavenger molecule dissolved conventionally in the oil-water emulsion of the interlayer for the prevention of colour contamination, because the migration of oxidised developer molecules from one colour recording layers into another is prevented much more efficiently.
According to the invention it has been found that the applicable range of scavenger modified polymer is much smaller than taught by the Japanese patent application cited hereinabove, because at the low scavenger modified polymer concentration and inter layer thickness from the disclosed application significant colour contamination happens which destroys the quality of the photographic image while at higher scavenger modified polymer concentrations the maximum density Dmax drops which is unacceptable for colour reproduction as well. This reduction of the maximum density Dmax was not recognised at all in the said patent application.
An advantage of the present invention is the improvement of sharpness because there is no oil present anymore to scatter the light. Moreover, the image sharpness can be maximized by using the interlayer design parameter to minimize the thickness of the interlayer.
Other effects and advantages of the present invention will become apparent from the detailed descriptions below, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed.
Surprisingly it has been found that it is possible to find a specific concentration range of the scavenger moieties attached to the modified polymer molecules (called [scavenger]) in combination with a specific thickness (called d) of the interlayer between the different colour recording layers which are combined into an interlayer design parameter {[scavenger moiety].d2} that defines the scavenging of the migrated oxidised developer molecules from a colour recording layer into the interlayer. The values of the design parameter can be chosen to meet color mix requirements of the light recording material without resulting in detrimental effects on the other photographic properties as the maximum density Dmax, while dye fading and the sharpness of each colour recording layer improve. It is well known to an expert in the field that for some light recording materials it is desirable to have a certain small amount of color mix to improve the color reproduction quality of said material.
In particular the invention is based thereon that the design parameter {[scavenger moiety].d2} is not lower than 2*10xe2x88x9215 mmol m2/g, since lower values give rise to unacceptable colour mix. Preferably this value is larger than 5*10xe2x88x9215 mmol m2/g, since for these values minor amounts of colour mix can be used to improve image quality in some cases. Most preferably this value is larger than 10*10xe2x88x9215 mmol m2/g, in order to effectively prevent oxidised developer diffusion and hence to reach an acceptable level of color mix.
Moreover the invention is based thereon that no decrease of the Dmax was found when the concentration of the scavenger moieties attached to the water soluble polymer does not exceed 0.5, preferably 0.30, most preferred 0.15 mmol/g otherwise also the oxidised developer molecules in the colour recording layers will be scavenged which results in a drop of the maximum density Dmax of each colour recording layer.
According to the invention it has thus become possible to provide on one hand a scavenger modified polymer in the interlayer which scavenges oxidised developer molecules more effectively at the same maximum density Dmax of each colour recording layer if the interlayer design parameter {[scavenger moiety].d2}, preferably, remains smaller than 700*10xe2x88x9215 mmol m2/g polymer for the interlayers than applying the scavenger molecules in the conventional oil-water emulsions.
Most preferably the interlayer design parameter {[scavenger moiety].d2} for the interlayers between the color recording layers remains within the range of 40*10xe2x88x9215 mmol m2/g polymer and 250*10xe2x88x9215 mmol m2/g polymer.
As was already stated herein-above, one of the additional advantages of the present invention is, that photographic material can be provided having one or more interlayers, with a thickness and scavenger concentration that is exactly tuned. This provides for photographic materials having thinner interlayers, which thus may produce sharper images. In fact. it was found that material, such as photographic film or paper, can be provided in which the thickness of the interlayer is up to 30-50% less than the thickness of interlayers in conventional materials. In conventional photographic materials, usually the dry thickness of the interlayer is larger than 1.5 xcexcm. According to the present invention, however, thicknesses of less than 1.5 xcexcm, preferably less than 1.0 xcexcm, may be obtained. The use of thinner interlayers provides for the distinct advantages that photographic material is obtained that gives much sharper images, while the specifications of the material with respect to Dmax and color mix are maintained.
The small ranges of the interlayer design parameter {[scavenger moiety].d2} in our invention as compared with the large concentration range of the scavenger modified polymers as disclosed in JP-4062548 A, indicate that the prior-art patent does not take into account the detrimental effect on most important photographic qualities like the colour contamination and the maximum density Dmax as our invention shows outside the specified limits of the interlayer design parameter {[scavenger moiety].d2} Moreover, JP-4062548 A is silent with respect to layer thicknesses.
The scavenger molecules to be used for the chemical linking with the polymers to be applied in the interlayer of the photographic product are selected from the scavenger molecules which are conventionally also used in the photographic oil-water emulsion of the interlayers. The molecular structure of the scavenger molecules is based upon a cresol type of molecule, a pyrogallol type, a cathechol type, a hydrochinon type or a 2,4-disulphonamidophenol type. More typical examples of scavenger molecular structures are shown in the figures attached hereto. The preferred scavenger structure for our invention is the 2,5-dihydroxybenzoic acid molecule.
The polymer molecules to be used for the chemical linking with the scavenger molecules, which are applied in the interlayers of the photographic products, are selected from the same molecules, which are conventionally used in the photographic oil-water emulsion of the interlayers. The molecular structure of the water soluble polymer molecules is selected from the group consisting of casein, albumin, sericin, soluble collagen, gelatine, polyvinyl alcohol, polyvinyl glycol, polyvinyl pyrrolidone, poly acrylamide, polyvinyl-imidazole, polyvinyl-pyrazole, cellulose derivatives, saccharine derivatives and the like. The preferred water soluble polymer structure for our invention is gelatine which can be obtained from natural gelatines, alkaline processed gelatine, acid processed gelatine, hydrolysed gelatine, peptised gelatine resulting from enzymatic treatment and recombinant gelatines.
The chemical linking between the activated carboxylic acid active groups of the scavenger molecules with the free amine groups of the polymers (like the pendant amine groups (lysine and hydroxy-lysine) of gelatine) is a well known synthesis route for the production of an amide, as is shown in disclosure EP-576911 A2. The activation of the carboxylic acid groups of the scavenger molecules can be carried out by various methods. In our example the method of N-hydroxy-succinimide (NHS)/DiCyclohexylCarbodiimide (DCC) in an organic solvent, such as organic solvent acetonitril, tetrahydrofuran, 1,3-dioxane or 1,4-dioxane, preferably tetrahydrofuran, has been used for activation. Another way to produce an amide is possible by linking the (activated) carboxylic acid end groups of gelatine amino acids (glutamine and asparagine) to the amine-moieties of the scavenger molecules.
The interlayers may be applied in various ways in the photographic material. At least one of said interlayers may consist of one homogeneous layer containing the said scavenger modified polymer or of a core layer with shield layers on both sides of the said core layer, in which each of the said shield layers contain a different concentration of the said scavenger modified polymer, or of a core layer containing the said scavenger modified polymer with shield layers on both sides of the said core layer, in which said shield layers do not contain a scavenger modified polymer.
As photographic supports photographic base paper is used which contains a polymer resin coated layer at the topside of the base paper and optionally at the backside of said base paper. At the topside above the polymer resin coated layer several photographic colour recording layers are coated in which the interlayers between the different colour recording layers contain the scavenger modified polymers which are described in this invention.
The invention of the scavenger modified polymers is also directed for various other photographic and movie products, e.g. photographic film, movie film and Reverse Colour Paper (RCP). Photographic film supports comprises films composed of polyethylene terephthalate, polyethylene naphthalate or triacetylcellulose and the like. At the topside of the film a multi-layer of different colour recording emulsion layers are coated which contain interlayers between the various colour recording layers comprising the invented scavenger modified polymers. Movie film also comprises the same support materials as photographic film, but the multi layer coating comprises other colour couplers and sensitisers. RCP comprises the same support as normal Colour Paper, but again, the colour recording layers comprise other colour couplers and other added components. As couplers use can be made of the couplers described, for example, in JP Patent 9-171240.
The processes and chemicals used in the development and bleaching processes are extensively described in the Research Disclosure 40145 of September 1997, Chapter XXIII: xe2x80x9cExposure and Processing, p 635-p 650. Preferred colour developing agents for colour paper are: 4-amino-3-methyl-N-ethyl-N-(b-hydroxyethyl)aniline sulphate, 4-amino-3-methyl-N-ethyl-N-(b-methanesulphonamidoethyl)aniline sesquisulphate hydrate and for colour film process the preferred developing agents are: o-, or p-amino phenol, p-phenylene diamine derivatives.